This invention relates to sulfurized products having utility as lubricant additives and lubricating compositions containing them. The invention also relates to a process for preparing sulfurized products, the products so prepared and lubricating compositions containing such products.
Antioxidant additives used in lubricating oils, particularly, but not exclusively, automotive lubricants, require a combination of properties which is difficult to meet in practice. Such additives must, of course, impart a high degree of resistance to oxidation to the lubricant, but in addition must be reasonably inexpensive, must be compatible with various other additives commonly used in lubricants, must have adequate thermal stability and must satisfy various other criteria of suitability, such as the ability to protect copper-lead bearings from corrosion. Very many different types of antioxidants have been proposed, and in some cases have been commercially used on a comparatively small scale. However, for many years the type of antioxidants which have been very widely used as the most suitable general purpose antioxidants for automotive and other lubricants are metal, particularly zinc, salts of di-hydrocarbyl dithiophosphoric acids.
However, the need for lubricant developments to keep pace with engine developments has given rise recently to difficulties in the use of metal dithiophosphate salts as antioxidants. The metal content of these additives is a source of ash and there is a growing tendency for the quality standards laid down by manufacturers and other interested organizations to specify low-ash lubricant formulations for modern engines. Attempts have been made to develop dithiophosphate derivatives, which do not contain metal, in order to meet these requirements. However, such developments have been forstalled, at least to some extent, by yet another development in engine design, namely, the use of catalytic devices in engine exhausts to minimize pollution caused by vehicle emissions. The catalysts used in such devices are sensitive to phosphorus compounds and can become poisoned and ineffective if exposed to such compounds. Consequently, the need has arisen for antioxidants which do not contain metal or phosphorus, and yet still meet all the requirements for antioxidants formerly satisfied by the metal dithiophosphates.
Sulfurized norbornenyl compounds are known and are reported by Kurtz et al., U.S. Pat. No. 3,586,700. Vulcanizing agents made by reaction of sulfur with diolefins such as dicyclopentadiene are reported by Mirviss, U.S. Pat. No. 3,523,926. German Pat. No. 658,128 discloses the reaction of unsaturated aliphatic compounds such as rubber with sulfur and hydrogen sulfide.